So I guess the last two storms to affect the Eastern Seaboard were described as classic Nor’easters where (correct me if I’m wrong) low pressure over I-95 sucks in warm moisture from (1) Gulf of Mexico (or (2) Outer Banks??), it collides with downward-moving cold air from Canada, and swoops along the coast from say N.C. to, who knows, Newfoundland (??).
Putting aside whether I got that right (though I welcome correction), how often can major snow affect the Northeast from (1) from the Northeast (my original mis-conception of Nor’easter was that it was a howling storm descending from Nova Scotia or wherever to Maine and then downward); (2) from the Midwest or from a Northwestern direction (blasting down from I don’t know, Minnesota; (3) from offshore, moving East to West; or (4) from nowhere, but just based on in situ moisture freezing and precipitating not as a front but as local weather?
I can’t answer all your questions, but remember there are at least two relevant directions. What direction is the storm moving and from what direction are the winds coming. The Nor’easter refers to the latter. Storm systems themselves generally travel from west to east (or northwest to southeast or southwest to northeast) due to the jet streams.
Storm systems come with low pressure areas and the winds rotate counter clockwise around a low (in the Northern Hemisphere). The typical Nor’easter hitting the New England coast would involve a storm passing from west to east a bit south of your location. First the winds will come from the southeast – but these will be bringing typically warmer southern air in. As the center of the storm passes, the winds will shift to the northeast bringing colder (and since they’ll be coming in off the Atlantic Ocean), moisture filled air. That’s when we get our big snows.
We, in New England, can also get snows if a storm comes from the southwest bringing moisture from the Atlantic or more typically the Gulf. As the air gets further north it cools and cannot hold as much moisture and dumps it out as snow or rain depending on the temperature.
OldGuy got it just right. The COLDEST storms in the Pennsylvania/Maryland/New York region and thereabouts tend to come from the northwest (originating in the Canadian Arctic)*, but the WETTEST ones tend to come from the southwest – humid Gulf of Mexico air masses that dump snow when they cool down to the dew point.
Incidentally, if you look at a globe or world map, you’ll notice that the other part of the world that has an arctic continent (to produce quick, driesh, cold blasts in early winter) to its northwest is the Korea/Manchuria/northern Japan region. It’s no coincidence that this is the other part of the world, besides New York/New England, which has spectacular autumn colors in its deciduous trees.
(*These Arctic storms pick up a little moisture as they cross the Great Lakes, but typically only enough to dump snow on places like Buffalo and Syracuse.)
Most of our weather in central Virginia seems to come from the Southwest; the Gulf of Mexico. However we did get one from the Northwest a few weeks ago.
Weather in the prevailing westerlies of the northern hemisphere generally moves from west to east. Ergo, most of the weather, including precipitation comes from either the NW or SW. From the NW, there is not much in the way of a source of precipitation. From the SW, there is the Gulf, and most of the storms are produced by an influx of Gulf moisture. The jet stream determines the paths of the storms. Now the jet stream affecting the east’s weather is streaming from the Gulf up the Atlantic seaboard; so, you have two sources of moisture: the Gulf and the Atlantic. When a low pressure does that, or when one forms off the coast of the Carolinas and swings along the coastline, the northeast gets its “Northeaster,” because of the counterclockwise circulation around the center of the low. The Atlantic is the source for the moisture, and since the Low is already east of the coast, cold weather is usually in place for heavy snows. Today, winter storm warnings were given all the way down to the Gulf, due to a low forming in the Gulf, following the jet stream. This should be another avenue for snowstorms in the northeast in a couple of days. This afternoon, a winter storm warning was given to the South Carolina coast, with 1-3 inches expected tomorrow evening, and possibly more right along the coast, closer to the center of the low.
Weather can also move from east to west if there is a tropical storm approaching. These storms originate in the horse latitudes (usually) where the prevailing winds are from east to west. Their paths are guided by the other pressure areas nearby. A high will block the ts from approaching, and a low moving w to e will cause the ts to follow its path. Sometimes the ts will join the barometric low and lose its tropical characteristics.
Yes, parts of southern Ontario are within the limits of the great-colors zone. The area around Sherbrooke, Quebec is the best in Canada, with the area around Fredericton, New Brunswick being a close second.
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